We had a commercial cow in the pasture do this very same thing back in August, limping, foot swollen, stinky smell, spot up on the side of the foot just like yours has that discharges puss. The vet said that it was hoof rot, (the first case of hoof rot ever on the place). Mom penned her, gave her large doses of LA 200, 3 times over a couple month period,put topical solution on foot, can't remember the name, it was purple in color, fed her sweet feed during the time that she was penned, had her in a three acre pasture that is actually what we call the baby nursery, she has since fully recovered, now she's back out in the pasture with the rest of the herd. I think we had her penned up for a couple of months. But, she's one of the best commercial cows that we have, so, the vet and feed bills will be recouped with her calf that she will have in March or April.